The role of antibodies (Abs) in preventing infection with HIV-1 has been firmly established by a multitude of passive immunization experiments in several animal models. However, developing an effective HIV vaccine inducing protective Abs is a major challenge for modern medicine. Past efforts yielded disappointing results with the exception of the RV144 vaccine trial. In recipients of the RV144 vaccine, high levels of plasma anti-V2 Abs correlate inversely with reduced risk of HIV-1 infection. However, whether the V2 antibodies directly protect against infection or whether the V2 Abs correlate with vaccine efficacy remains unknown. To address these questions, experiments in non-human primates are necessary, since this model has the most similar immune response to humans. Thus, we propose to study the various inhibitory functions of anti-V2 monoclonal Abs (mAbs) and the mechanistic effect of vaccine-induced mucosal anti-V2 Abs in rhesus macaques, i.e., whether these antibodies protect against SHIV challenge alone or in cooperation with other anti-HIV-1 envelope (Env) antibodies. We hypothesize that anti-V2 Abs inhibit the gp120/?4?7 integrin interaction and block binding of HIV-1 to Th17 cells expressing ?4?7, CD4 and CCR5. As Th17 cells are mainly located in the mucosal tissues, we predict that induction of anti-V2 Abs locally increases the titer of V2 Abs in mucosal secretions and more efficiently blocks virus binding to target T cells, resulting in protection against HIV-1 infection. To test this hypothesis, we will immunize rhesus macaques with V1V2 fusion protein to induce mucosal and systemic anti-V2 Abs compared to gp120 Abs and challenge the animals with SHIV to determine the protective potentials of V2 Abs. The possible inhibitory functions of anti-V2 Abs, including neutralization, Fc-mediated activities and inhibition the gp120/?4?7 interaction, will be tested using human V2 mAbs produced in our lab in both isotypes IgG1 and IgG3 (Aim 1). These studies will determine the type and range of inhibitory activities mediated by vaccine-induced mucosal and/or systemic anti-V2 Abs. The macaques will be immunized using gp120 DNA prime and protein boost including V1V2-fusion protein administered at mucosal tissues, systemically and compared to systemic gp120 with matching sequence of CM244 virus. The most representative inhibitory functions defined in Aim 1 will be used to monitor the development of vaccine-induced V2 Abs in serum and mucosal secretions (Aim 2). To determine vaccine efficiency, the immunized macaques with detected anti-V2 Abs in mucosal vaginal and rectal secretions will be challenged by multiple low doses of vaginal SHIV-BaL inoculation (Aim 3). The proposed study is designed to test whether anti-V2 antibodies have ability to protect from SHIV challenge or reduce the viral load and whether mucosal V2 antibodies have any advantage over systemic V2 antibodies. The results of this research will have practical consequences to inform the design of HIV vaccine to induce either a high titer of systemic anti-V2 Abs along with other Abs or include intranasal immunization to induce mucosal anti-V2 Abs to increase vaccine efficacy.